The purposes is to evaluate mental workload demand on an individual performing a specific task.
By more innovation systems/devices (ex. e-mirror) appear in vehicle, it also caused potential road safety issues. The design development have the responsibility to evaluate whether these innovative systems/devices really support the driving task or, on the contrary, lead to distraction and increase mental workload, with potential dramatic consequences in terms of road safety.
Workload can be defined as a cost incurred by a human operator to achieve a particular level of performance. Driving performance and the driver’s mental workload are both relevant and complementary parameters to consider, knowing that they can vary independently. If the complexity of driving task increases, the driver will increase workload effort to maintain a stable performance. So we should evaluate the driving performances, secondary driving task (ie. Look/search information from e-mirror) performances (objective data), and subjective workload (subjective data) simultaneously if we would like to confirm the effect of new design on dashcam /or e-mirror (ie. ADAS warning message design, etc..).
For objective data, driving performances can be measured & collected by driving trackers or be observed. Secondary driving task performances can be recorded by experimenters. For subjective workload measurement, the famous scale is NASA Task Load Index (NASA-TLX).
What is NASA-TLX
The NASA task load index (NASA TLX) is a tool for measuring and conducting a subjective mental workload assessment with various human-machine interface systems. Originally developed as a paper and pencil questionnaire by NASA Ames Research Center’s (ARC) Sandra Hart in the 1980s, NASA TLX has become the gold standard for measuring subjective workload across a wide range of applications.It rates performance across six dimensions to determine an overall workload rating. The six dimensions are as follows:
1. Mental demand - how much thinking, deciding, or calculating was required to perform the task.
2. Physical demand - the amount and intensity of physical activity required to complete the task.
3. Temporal demand - the amount of time pressure involved in completing the task.
4. Effort - how hard does the participant have to work to maintain their level of performance?
5. Performance - the level of success in completing the task.
6. Frustration level - how insecure, discouraged, or secure or content the participant felt during the task.
The TLX also uses a paired comparisons procedure. This involves presenting 15 pairwise combinations to the participants and asking them to select the scale from each pair that has the most effect on the workload. This procedure accounts for individual differences in workload definition and differences in the sources or workload between the tasks. The contents about NASA TLX can be referenced on website in detail.
Conclusion
In my several usage experiences, I think it provides a quick and simple estimate of operator mental workload and allow to be used in multiple domains. It also had app version, and increased the use convenience by mobile device. But I think it need to spend more time to conduct the subscale weighting, and maybe intrusive to the task when conducted in test. In addition, the participants may forget details of the task when conducted after task.
Although users of this tool usually have some training or experience in its use, NASA TLX has become the gold standard for measuring subjective workload across a wide range of applications. It also had app version, and increased the use convenience by mobile device.
If you are interested in this tool, you can go to learn more:
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